Gas turbine engine shaft bearing configuration

ABSTRACT

A gas turbine engine includes a housing includes an inlet case and an intermediate case that respectively provide an inlet case flow path and an intermediate case flow path. A rotor is connected to the hub and supports a compressor section. The geared architecture includes an epicyclic gear train. A fan is rotationally driven by the geared architecture. First and second bearings support the shaft relative to the intermediate case and the inlet case, respectively. The radially inner boundary of the core inlet is at a location of a core inlet stator and the radially inner boundary of the compressor section inlet is at a location of the first stage low-pressure compressor rotor.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No. 14/219,112 filed on Mar. 19, 2014, which is a continuation of U.S. application Ser. No. 14/012,773, filed on Aug. 28, 2013, now U.S. Pat. No. 8,863,491 issued Oct. 21, 2014, which claims priority to U.S. Provisional Application No. 61/860,337 filed Jul. 31, 2013, and is a continuation-in-part of U.S. application Ser. No. 13/904,416 filed on May 29, 2013, which is a continuation of U.S. application Ser. No. 13/762,970 filed on Feb. 8, 2013, now U.S. Pat. No. 8,511,061 issued Aug. 20, 2013, which is a continuation of U.S. application Ser. No. 13/362,170 filed on Jan. 31, 2012, now U.S. Pat. No. 8,402,741 issued Mar. 26, 2013.

BACKGROUND

Turbomachines, such as gas turbine engines, typically include a fan section, a turbine section, a compressor section, and a combustor section. The fan section drives air along a core flow path into the compressor section. The compressed air is mixed with fuel and combusted in the combustor section. The products of combustion are expanded in the turbine section.

A typical jet engine has two or three spools, or shafts, that transmit torque between the turbine and compressor sections of the engine. Each of these spools is typically supported by two bearings. One bearing, for example, a ball bearing, is arranged at a forward end of the spool and is configured to react to both axial and radial loads. Another bearing, for example, a roller bearing is arranged at the aft end of the spool and is configured to react only to radial loads. This bearing arrangement fully constrains the shaft except for rotation, and axial movement of one free end is permitted to accommodate engine axial growth.

A core inlet typically controls flow of air into the core flow path. The flow of air moves from the core inlet to a compressor section inlet. The relative radial positions of the core inlet and the compressor section inlet may influence flow through the core and a profile of the turbomachine.

SUMMARY

In one exemplary embodiment, a gas turbine engine includes a shaft providing a rotational axis. A hub is operatively supported by the shaft. A housing includes an inlet case and an intermediate case that respectively provide an inlet case flow path and an intermediate case flow path. A rotor is connected to the hub and supports a compressor section. The compressor section is arranged axially between the inlet case flow path and the intermediate case flow path. The rotor is a first stage rotor of a low-pressure compressor. A core inlet has a radially inner boundary that is spaced a first radial distance from the rotational axis. A compressor section inlet has a radially inner boundary that is spaced a second radial distance from the rotational axis. A geared architecture is arranged within the inlet case. The geared architecture includes an epicyclic gear train. The geared architecture includes a torque frame that is secured to the inlet case. The torque frame supports multiple circumferentially arranged star gears intermeshing with a sun gear. The shaft includes a main shaft and a flex shaft. The flex shaft has a first end and a second end. The first end is secured to the main shaft and the sun gear is supported on the second end. A fan is rotationally driven by the geared architecture. First and second bearings support the shaft relative to the intermediate case and the inlet case, respectively. The radially inner boundary of the core inlet is at a location of a core inlet stator and the radially inner boundary of the compressor section inlet is at a location of the first stage low-pressure compressor rotor.

In a further embodiment of the above, an inlet flow of the compressor section is configured to be from about 30 lb/sec/ft² to about 37 lb/sec/ft² when the engine is operating at a cruise speed.

In a further embodiment of any of the above, a turbine inlet temperature of a high-pressure turbine within the engine is configured to be from about 2,000° F. to about 2,600° F. when the engine is operating at a cruise speed.

In a further embodiment of any of the above, a tip speed of a blade array in the compressor section during engine operation is configured to be from about 1,050 ft/sec to about 1,350 ft/sec.

In a further embodiment of any of the above, the geared architecture has a gear reduction ratio of greater than about 2.3.

In a further embodiment of any of the above, the geared architecture further includes a ring gear arranged circumferentially about and intermeshing with the star gears. The ring gear drives a fan shaft and the fan shaft rotationally drives the fan.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure can be further understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

FIG. 1 schematically illustrates an embodiment of a gas turbine engine.

FIG. 2 is a cross-sectional view of a front architecture of the gas turbine engine embodiment shown in FIG. 1.

FIG. 3 shows a close-up view of a core inlet portion of the FIG. 1 gas turbine engine embodiment.

The embodiments, examples and alternatives of the preceding paragraphs, the claims, or the following description and drawings, including any of their various aspects or respective individual features, may be taken independently or in any combination. Features described in connection with one embodiment are applicable to all embodiments, unless such features are incompatible.

DETAILED DESCRIPTION

FIG. 1 schematically illustrates a gas turbine engine 20. The gas turbine engine 20 is disclosed herein as a two-spool turbofan that generally incorporates a fan section 22, a compressor section 24, a combustor section 26 and a turbine section 28. Alternative engines might include an augmentor section (not shown) among other systems or features. The fan section 22 drives air along a bypass flowpath B while the compressor section 24 drives air along a core flowpath C (as shown in FIG. 2) for compression and communication into the combustor section 26 then expansion through the turbine section 28. Although depicted as a two-spool turbofan gas turbine engine in the disclosed non-limiting embodiment, it should be understood that the concepts described herein are not limited to use with two-spool turbofans as the teachings may be applied to other types of turbine engines including three-spool architectures.

The exemplary engine 20 generally includes a low speed spool 30 and a high speed spool 32 mounted for rotation about an engine central longitudinal axis A relative to an engine static structure 36 via several bearing systems 38. It should be understood that various bearing systems 38 at various locations may alternatively or additionally be provided, and the location of bearing systems 38 may be varied as appropriate to the application.

The low speed spool 30 generally includes an inner shaft 40 that interconnects a fan 42, a low pressure compressor 44 and a low pressure turbine 46. The inner shaft 40 is connected to the fan 42 through a speed change mechanism, which in exemplary gas turbine engine 20 is illustrated as a geared architecture 48 to drive the fan 42 at a lower speed than the low speed spool 30. The high speed spool 32 includes an outer shaft 50 that interconnects a high pressure compressor 52 and high pressure turbine 54. A combustor 56 is arranged in exemplary gas turbine 20 between the high pressure compressor 52 and the high pressure turbine 54. A mid-turbine frame 57 of the engine static structure 36 is arranged generally between the high pressure turbine 54 and the low pressure turbine 46. The mid-turbine frame 57 supports one or more bearing systems 38 in the turbine section 28. The inner shaft 40 and the outer shaft 50 are concentric and rotate via bearing systems 38 about the engine central longitudinal axis A, which is collinear with their longitudinal axes.

The core airflow C is compressed by the low pressure compressor 44 then the high pressure compressor 52, mixed and burned with fuel in the combustor 56, then expanded over the high pressure turbine 54 and low pressure turbine 46. The mid-turbine frame 57 includes airfoils 59 which are in the core airflow path. The turbines 46, 54 rotationally drive the respective low speed spool 30 and high speed spool 32 in response to the expansion. It will be appreciated that each of the positions of the fan section 22, compressor section 24, combustor section 26, turbine section 28, and fan drive gear system 48 may be varied. For example, gear system 48 may be located aft of combustor section 26 or even aft of turbine section 28, and fan section 22 may be positioned forward or aft of the location of gear system 48.

The engine 20 in one example a high-bypass geared aircraft engine. In a further example, the engine 20 bypass ratio is greater than about six (6), with an example embodiment being greater than ten (10). The example speed reduction device is a geared architecture 48 however other speed reducing devices such as fluid or electromechanical devices are also within the contemplation of this disclosure. The example geared architecture 48 is an epicyclic gear train, such as a star gear system or other gear system, with a gear reduction ratio of greater than about 2.3, or more specifically, a ratio of from about 2.2 to about 4.0. In one disclosed embodiment, the engine 20 bypass ratio is greater than about ten (10:1), the fan diameter is significantly larger than that of the low pressure compressor 44, and the low pressure turbine 46 has a pressure ratio that is greater than about 5:1. Low pressure turbine 46 pressure ratio is pressure measured prior to inlet of low pressure turbine 46 as related to the pressure at the outlet of the low pressure turbine 46 prior to an exhaust nozzle. It should be understood, however, that the above parameters are only exemplary of one embodiment of a geared architecture engine and that the present invention is applicable to other gas turbine engines including direct drive turbofans.

A significant amount of thrust is provided by the bypass flow B due to the high bypass ratio. The fan section 22 of the engine 20 is designed for a particular flight condition—typically cruise at about 0.8 Mach and about 35,000 feet (10.67 km). The flight condition of 0.8 Mach and 35,000 ft (10.67 km), with the engine at its best fuel consumption—also known as bucket cruise Thrust Specific Fuel Consumption (“TSFC”). TSFC is the industry standard parameter of lbm of fuel being burned divided by lbf of thrust the engine produces at that minimum point. “Low fan pressure ratio” is the pressure ratio across the fan blade alone, without a Fan Exit Guide Vane (“FEGV”) system. The low fan pressure ratio as disclosed herein according to one non-limiting embodiment is less than about 1.45. “Low corrected fan tip speed” is the actual fan tip speed in ft/sec divided by an industry standard temperature correction of [(T_(ambient) ° R)/518.7° R)^(0.5)]. The “Low corrected fan tip speed” as disclosed herein according to one non-limiting embodiment is less than about 1150 ft/second (350 m/second).

Referring to FIG. 2, a core housing 60 includes an inlet case 62 and an intermediate case 64 that respectively provide an inlet case flowpath 63 and a compressor case flowpath 65. In other embodiments, the core housing may include additional cases. Similarly, the compressor section as a whole may include any number of cases. Together, the inlet and compressor case flowpaths 63, 65, in part, define a core flowpath through the engine 20, which directs a core flow C.

The intermediate case 64 includes multiple components, including the intermediate case portion 66, and the bearing support 68 in the example, which are removably secured to one another. The bearing support portion 68 has a first bearing 70 mounted thereto, which supports the inner shaft 40 for rotation relative to the intermediate case 64. In one example, the first bearing 70 is a ball bearing that constrains the inner shaft 40 against axial and radial movement at a forward portion of the inner shaft 40. The first bearing 70 is arranged within a bearing compartment 71.

In the example, the inner shaft 40 is constructed of multiple components that include, for example, a main shaft 72, a hub 74 and a flex shaft 76, which are clamped together by a nut 80 in the example. The first bearing 70 is mounted on the hub 74 (i.e., low pressure compressor hub). The flex shaft 76 includes first and second opposing ends 82, 84. The first end 82 is splined to the hub 74, and the second end 84 is splined to and supports a sun gear 86 of the geared architecture 48. Bellows 78 in the flex shaft 76 accommodate vibration in the geared architecture 48.

The geared architecture 48 includes star gears 88 arranged circumferentially about and intermeshing with the sun gear 86. A ring gear 90 is arranged circumferentially about and intermeshes with the star gears 88. A fan shaft 92 is connected to the ring gear 90 and the fan 42 (FIG. 1). A torque frame 94 supports the star gears 88 and grounds the star gears 88 to the housing 60. In operation, the inner shaft 40 rotationally drives the fan shaft 92 with the rotating ring gear 90 through the grounded star gears 88.

The low pressure compressor 44 includes multiple compressor stages arranged between the inlet and intermediate case flowpaths 63, 65, for example, first and second compressor stages 98, 100, that are secured to the hub 74 by a rotor 96. The first bearing 70 is axially aligned with one of the first and second compressor stages 98, 100. In one example, a variable stator vane array 102 is arranged upstream from the first and second compressor stages 98, 100. Struts 104 are arranged upstream from the variable stator vane array 102. An array of fixed stator vanes 106 may be provided axially between the first and second compressor stages 98, 100. Although a particular configuration of low pressure compressor 44 is illustrated, it should be understood that other configurations may be used and still fall within the scope of this disclosure.

The inlet case 62 includes inlet case portions 108, and bearing support 110, which are removably secured to one another. The bearing support portion 110 and torque frame 94 are secured to the inlet case portion 108 at a joint 109. The bearing support portion 110 supports a second bearing 112, which is a rolling bearing in one example. The second bearing 112 is retained on the hub 74 by a nut 113, for example, and is arranged radially outward from the flex shaft 76 and radially between the torque frame 94 and flex shaft 76. In the example, the second bearing 112 is axially aligned with and radially inward of the variable stator vane array 102. The geared architecture 48 and the second bearing 112 are arranged in a lubrication compartment 114, which is separate from the bearing compartment 71 in the example.

Referring now to FIG. 3 with continued reference to FIG. 1, the core flow path of the example engine 20 begins at a core inlet 160 and extends through and past the low-pressure compressor 44. The core inlet 160 has a radially inner boundary 162 and a radially outer boundary 166.

A core inlet stator 170 is located at or near the core inlet 160. The core inlet stator 170 attaches to a core case 174 at the radially inner boundary 162. The core inlet stator 170 attaches to an inlet case 178 at the radially outer boundary 166. The core inlet stator 170 extends radially across the core flow path C.

In this example, the radially inner boundary 162 is positioned a radial distance D₁ from the axis A. The distance D₁, in this example, also corresponds to the radial distance between a root 164 of the core inlet stator 170 and the axis A. In this example, the root 164 of the core inlet stator 170 is radially aligned with the radially inner boundary 162 of the core flow path C.

After flow moves through the core inlet 160, the flow moves through a compressor inlet 182 into the compressor section 24. In this example, the compressor section inlet 182 is an inlet to the low-pressure compressor 44 of the compressor section 24. The compressor inlet 182 extends from a radially inner boundary 186 to a radially outer boundary 190.

Notably, a blade 198 of a rotor within the low-pressure compressor 44 extends from a root 202 to a tip 206. The blade 198 is located at or near the compressor inlet 182. The blade 198 part of a compressor rotor within a first stage of the compressor section 24. The blade 198 is thus part of a first stage rotor, or a leading blade of the compressor section 24 relative to a direction of flow along the core flow path C.

In some examples, the blade 198 represents the axial position where air enters the compressor section 24 of the core flow path C. The blade 198 extends radially across the core flow path C.

The radially inner boundary 186 is positioned a radial distance D₂ from the axis A. The distance D₂, in this example, also corresponds to the radial distance between the root 202 of the blade 198 and the axis A. In this example, the root 202 is radially aligned with the radially inner boundary 186 of the core flow path C.

In the example engine 20, a preferred ratio range of the distance D₂ to the distance D₁ spans from about 0.65 to about 0.9, which provides a relatively low profile core flow path contour. High profile flow path contours have greater differences between D₂ and D₁, and thus larger “humps” between the core inlet 160 and the compressor inlet 182. High profile flow path contours introduce discontinuities that undesirably disrupt the airflow and undesirably add weight to the engine 20. The ratio range of about 0.65 to about 0.9 is made possible, in part, by the incorporation of the geared architecture 48 into the engine 20. The “hump” in this example is generally area 200. Additionally, since at least one of the first and second bearings 70, 112 are packaged radially inward of the low pressure compressor 44, the distance D₂ may be larger as compared to bearing arrangements which have bearings axially offset from the compressor section. Thus, the axially compact low pressure compressor and bearing arrangement also minimizes discontinuities in the flow path contour while reducing the axial length of the engine.

Other characteristics of the engine having this ratio may include the engine 20 having a specific inlet flow of the low pressure compressor at cruising speeds to be between about 30 lb/sec/ft² and about 37 lb/sec/ft². The specific inlet flow is the amount of flow moving into the compressor section 24 and specifically, in this example, into a compressor inlet 182 and through the compressor section 24.

Another characteristic of the example engine 20 is that the cruise speeds of the example engine are generally Mach numbers of about 0.7 to about 0.9.

Yet another characteristic of the engine 20 is that a temperature at an inlet to the high-pressure turbine 54 may be from about 2,000° F. (1093.33° C.) to about 2,600° F. (1426.66° C.). Maintaining temperatures within this range balances good fuel consumption, low engine weight, and low engine maintenance costs.

Yet another characteristic of the engine 20 is that a tip speed of blades in a rotor of the low-pressure compressor 44 (a compressor rotor) may be from about 1,050 fps (320 m/s) to about 1,350 fps (411 m/s).

In this example, the geared architecture 48 of the engine 20 may have a gear ratio of greater than about 2.3, or more specifically, a ratio of from about 2.2 to about 4.0.

It should also be understood that although a particular component arrangement is disclosed in the illustrated embodiment, other arrangements will benefit herefrom. Although particular step sequences are shown, described, and claimed, it should be understood that steps may be performed in any order, separated or combined unless otherwise indicated and will still benefit from the present invention.

Although the different examples have specific components shown in the illustrations, embodiments of this invention are not limited to those particular combinations. It is possible to use some of the components or features from one of the examples in combination with features or components from another one of the examples.

Although an example embodiment has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of the claims. For that reason, the following claims should be studied to determine their true scope and content. 

What is claimed is:
 1. A gas turbine engine comprising: a shaft assembly providing a rotational axis; a hub operatively supported by the shaft assembly; a housing including an inlet case and an intermediate case that respectively provide an inlet case flow path and an intermediate case flow path; a rotor connected to the hub and supporting a compressor section, the compressor section arranged axially between the inlet case flow path and the intermediate case flow path, the rotor is a first stage rotor of a low-pressure compressor; a core inlet has a radially inner boundary that is spaced a first radial distance from the rotational axis, and a compressor section inlet having a radially inner boundary that is spaced a second radial distance from the rotational axis; a geared architecture arranged within the inlet case, the geared architecture including an epicyclic gear train, the geared architecture includes a torque frame secured to the inlet case, the torque frame supports multiple circumferentially arranged star gears intermeshing with a sun gear, the shaft assembly includes a main shaft and a flex shaft, and the flex shaft has a first end and a second end, the first end secured to the main shaft and the sun gear supported on the second end; a fan rotationally driven by the geared architecture; first and second bearings supporting the shaft assembly relative to the intermediate case and the inlet case, respectively, the first and second bearings each including a bearing race configured to rotate at a same rotational speed as the shaft assembly; and wherein the radially inner boundary of the core inlet is at a location of a core inlet stator and the radially inner boundary of the compressor section inlet is at a location of the first stage low-pressure compressor rotor.
 2. The gas turbine engine according to claim 1, wherein a tip speed of a blade array in the compressor section during engine operation is configured to be from 1,050 ft/sec to 1,350 ft/sec.
 3. The gas turbine engine according to claim 1, wherein the geared architecture further includes a ring gear arranged circumferentially about and intermeshing with the star gears, the ring gear driving a fan shaft, and the fan shaft rotationally driving the fan. 